The present invention relates to an optical filter device which is disposed in an optical path to separate a desired wavelength component or components from optical energy propagating therethrough and, more particularly, to an optical filter device which is desirably applicable to optical energy having high energy densities.
As well known in the art, optical energy such as the solar energy or the energy of artificial light may be converged by lenses or the like into light conducting cables, or fiber optic cables, to propagate therethrough to desired locations. The converged optical energy is usable for lighting and other various applications. Such a technique has been implemented by, for example, an artificial light source apparatus in which an artificial light source is disposed in a housing and optical energy emanating from the light source is converged by a lens to reach a light receiving end of a light conducting cable, which is located in another housing, as disclosed in Japanese Patent Application No. 56-11153 by way of example.
While the conducted optical energy may be used with all the wavelength components contained therein, a specific component or components of the optical energy may be separated from the others to be used for particular applications. For example, the applicant has proposed the use of optical energy conducted by a light conductor as described as a light source for photosynthesis, typically cultivation of chlorella or forcing culture of plants. For photosynthetic reactions, ultraviolet rays, infrared rays and like components contained in optical energy are harmful. A solution to such a problem may be the use of an optical filter which intercepts the ultraviolet, infrared and other undesirable light components contained in the conducted optical energy while transmitting visible light component only. However, concerning filters for such applications, problems have existed in that they undergo thermal destruction or deterioration due to the considerable energy density of the conducted light, in that the ultraviolet, infrared and other components undesirable for a particular application are simply wasted to limit the efficiency of optical energy utilization.